In a scanning electron microscope (SEM) representing one type of a charged particle beam apparatus, an observation method has been known which makes use of electrification generated by irradiation of an electron beam. Available as an observation objective using the observation method is, for example, a contact hole of a semiconductor device. With the semiconductor device rendered corpuscular, the aspect ratio (ratio of depth to diameter) of the hole has been tending to increase. When observation of a hole having an aspect ratio of, for example, 20 is considered, the possibility that electrons given off from the bottom of hole will impinge upon the side wall of the hole increases and detection of the electrons fails, making it sometimes difficult to observe the shape of hole bottom.
The observation method making use of the electrification is used exemplarily to pull up electrons given off from the bottom of hole. In order to pull up secondary electrons generated at the hole bottom, a pull-up electric field needs to be formed by applying a positive electrification to the outer surface (entrance) of the hole. For this purpose, an electron beam irradiation is carried out through pre-dosing (preliminary irradiation) apart from observation by using a beam being at a low magnification or having a larger efficiency of discharging secondary electrons (electrons discharged from a sample/electrons incident to the sample) as compared to a beam for observation, thus applying the positive electrification.
When conducting ordinary observation after the positive electrification has been applied, secondary electrons generated at the hole bottom are pulled up to the outside of the hole with the help of the pull-up electric field formed by the positive electrification at the surface. By detecting the electrons, the shape of the hole bottom can be observed. In Patent Literatures 1 to 4, an observation method is explained in which after electrification has been deposited on a sample by preliminary irradiation based on electron beam irradiation, a beam dedicated to observation is irradiated.